Theta (Θ θ) in LaTeX
In LaTeX, \theta gives the lowercase theta (θ) and \Theta gives the uppercase theta (Θ), both in maths mode; \vartheta produces the curly variant (ϑ).
LaTeX command
\ThetaNot the symbol you meant? Draw it to find the command →
Lowercase theta, \theta, is the default symbol for an angle in geometry and trigonometry and for the polar and azimuthal coordinates in polar and spherical systems. In statistics it is the generic name for an unknown parameter to be estimated, often paired with a hat as \hat{\theta}. All three commands, \theta, \Theta and \vartheta, must be used in maths mode.
Uppercase theta, \Theta, has its own roles: the Heaviside step function is often written \Theta(x), a Debye or characteristic temperature is \Theta, and in the analysis of algorithms \Theta(n) denotes an asymptotically tight bound, the companion of big-O. The letter is a circle bisected by a horizontal stroke.
The variant \vartheta gives the cursive form (ϑ), useful when you need a second theta-like symbol distinct from \theta in the same document, for instance a separate angle or a Jacobi theta function. Both forms are standard LaTeX and render in KaTeX without extra packages.
Other forms
\thetalowercase theta\Thetauppercase theta (Θ)\varthetacurly / variant formExamples
$\theta$lowercase theta inline
$\sin^2\theta + \cos^2\theta = 1$an angle in the Pythagorean identity
$\Theta$uppercase theta
$T(n) = \Theta(n \log n)$a tight asymptotic bound
$\vartheta$the curly variant
Tips and common mistakes
- Use
\thetafor angles and parameters,\Thetafor the step function, a Debye temperature or a tight asymptotic bound. \varthetais the cursive variant; reach for it when you need a theta distinct from\thetaon the same page.- There is no space needed in
\sin\theta; the\sinoperator inserts the correct thin space before its argument. - All theta commands require maths mode; wrap them in .
- For a bold theta (a parameter vector) use
\boldsymbol{\theta}, not\mathbf, which does not bold lowercase Greek letters.
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What is the difference between \theta and \vartheta?
\theta is the standard straight-backed theta (θ); \vartheta is the cursive variant (ϑ). They are the same letter, so pick one and use the other only when you need a visually distinct second symbol.
How do I write a capital theta?
Use \Theta, which renders Θ. It is commonly used for the Heaviside step function and for big-Theta asymptotic notation.
How do I make theta bold?
Use \boldsymbol{\theta} (needs the amsmath or bm package in a document). \mathbf does not affect lowercase Greek letters.